Just managed to update router to latest FW 1.0.9.4 and all seems to be working fine on 100/20 fibre. First time yesterday I tried it just spun its wheels for a few minutes then gave an "update failed" message. Rebooted and same message. Today I unchecked "Allow DHCP options 66 and 43 override" then rebooted, hit "upgrade now", rebooted again and it worked.

Still can't update the 7610 AP as it still gives "update failed" message, so sometime I will unpair it, factory reset, do the update, then re-pair with router. Meantime everything is working with AP on 1.0.6.43. Speedtests from PC and wifi are both approx 100/20, so it seems that all's well that ends well.